Organic thin-film light emitting devices are known to be exquisitely sensitive to water vapor and oxygen. Exposure to either of these materials results in the rapid degradation and failure of the devices, reducing or destroying the utility of the flat panel display or flat panel illumination source utilizing these devices. A number of approaches have been developed to seal the organic thin-film devices to eliminate exposure to oxygen and water vapor. The most commonly used approach in commercial application is to apply an adhesive between the substrate and a cover and then use a variety of means, such as UV exposure to accelerate the curing of the adhesive.
A key limitation of this approach lies in dispensing a controlled bead of adhesive such that the adhesive bead contains neither too much adhesive, nor too little adhesive. If too much adhesive is present the excess may flow into the active display or electronic areas when the substrate and cover are squeezed together. If too little adhesive is present, this may result in gaps in the perimeter seal.
Prior art discloses the use of etched features in the cap or substrate which can help limit the spread of adhesive in a direction perpendicular to the axis of the seal. Patent WO 02/21557 A1 discloses the use of a sealing dam etched into the glass substrate. The sealing dam not only provides appropriate spacing between the substrate and the cap, but also prevents the adhesive from flowing into the device area and damaging the display medium. Publication 2003/0007117 A1 discloses the use of an etched channel in the substrate or cap providing a reservoir of extra volume for adhesive to flow into during assembly thereby preventing the adhesive seal from encroaching into the display area of the device. Etching processes, however, can add significant cost to the overall device, and furthermore dictate the use of thicker materials in order to provide sufficient depth to form the encapsulating features.
There is a need therefore, for an improved method for encapsulating an area on a substrate which provides well defined, high quality sealing features without the use of an expensive etching processes.